The present invention relates to a thin-film magnetic head formed by stratified build-up on a nonmagnetic substrate for recording into a recording medium which is provided with a magnetizable storage layer, and into which information can be written along a track by perpendicular or vertical magnetization of the storage layer. Such a magnetic head comprises a ring-head-like magnetic conduction body for carrying magnetic flux having two magnet legs, the poles of which facing the recording medium are arranged in tandem, as seen in the direction of motion of the head, and which have a predetermined spacing from each other. Such heads further contain an at least largely flat coil winding, the turns of which extend through a space formed between the magnet legs. Such a magnetic head is shown in European Patent Application EP No. 0 012 910 A1, for example.
The principle of perpendicular magnetiziaiton for storing informaiton is generally known. See, for instance, IEEE Transactions on Magnetics, vol. MAG-16, no. 1, January 1980, pages 71 to 76; DE-OS No. 29 24 013; U.S. Pat. No. 4,287,544; or the above cited European Patent Application. This principle, which is frequently also called vertical magnetization, utilized special recording media in the form of rigid magnetic storage discs, flexible individual discs (floppy discs) or magnetic tapes. The recording medium has at least one magnetizable storage layer of predetermined thickness which contains a magnetically anisotropic material, especially of a CoCr alloy. The axis of the so-called easy magnetization of this layer points perpendicularly to the surface of the medium. By means of a special magnetic head, the individual pieces of information are then recorded along a track in successive sections, also called cells or blocks, by appropriate magnetization of the storage layer. In practice, the magnetic flux changes, i.e., the transitions from one direction of magnetization to the opposite one, are generally used as information. The sections have a predetermined dimension, also called wavelength, in the longitudinal direction of the track. As compared with the limit which is required by the method of longitudinal or horizontal storage by demagnetization, this dimension can be substantially smaller. Thus, the information density in the recording medium advantageously can be increased according to the principle of perpendicular magnetization.
The combined read-and-write heads, i.e., those with which both a write as well as a read function can be executed, and which are known for use with the principle of longitudinal magnetization, however, cannot be used directly also for perpendicular magnetization. If these heads, which generally have the shape of ring heads, are used, the conduction of the flux generally desired also for use with the principle of perpendicular magnetization, for a circuit closed as far as possible, can be achieved with low magnetic resistance. However, writing of both poles of these ring heads can then scarcely be suppressed, so that similar difficulties result in reading the written information.
One is therefore compelled to develop special write and read heads which use the principle of perpendicular magnetization. A magnetic head suitable therefor generally comprises a so-called main pole, by which a perpendicular magnetic field sufficiently strong for remagnetizing the individual sections of the storage layer is produced The required magnetic return can then be accomplished, for instance, by a so-called auxiliary pole on the opposite side of the recording medium. See the above-mentioned literature reference, IEEE Trans. Magn., vol. MAG-16. A magnetic return can also be made with a separate auxiliary pole which is located on the same side as the main pole. See IEEE Trans. Magn. vol. MAG-17, no. 6, November 1981, pages 3120 to 3122, or vol. MAG-18, no. 6, November 1982, pages 1158 to 1163 or the above cited patent publications. Accordingly, the magnetic write and read head known from the above mentioned European patent application contains a ring-head-like conducting body of two magnet legs which carries the magnetic flux, the ends of which, facing the recording medium, form a main and an auxiliary pole, and which are arranged in tandem as seen in the direction of motion of the head and at a predetermined distance from each other. The turns of an at least largely planar coil winding extend through a space which is formed between these two magnet legs, the space being filled with an insulating material. With this winding, the main pole is excited for the writing function and for the read function, the excitation of the main pole is measured. The turns of this winding as well as the magnet legs are applied by thinfilm technology on a nonmagnetic substrate.
In the magnetic-head type known, for instance, from the above patent documents, the auxiliary pole serves in any case only for returning the magnetic flux. Cross writing of the auxiliary pole can possibly be tolerated because the recording main pole always lags it and therefore over-writes information possibly written by the auxiliary pole. In order, however, to prevent, at least largely, concurrent reading of the auxiliary pole with its trailing edge, the so-called air gap formed between the two poles would have to be relatively wide so that a far-reaching reduction of the magnetic flux density at the auxiliary pole can be ensured. Suitably wide gap layers, however, can be realized by the thin-film technique only with difficulty.
Because of these difficulties, magnetic heads have also been proposed in which the use of a separate auxiliary pole is dispensed with. See IEEE Trans. Magn., vol. MAG-18, no. 6, November 1982, pages 1170 to 1172; EP No. 0 071 489 A2. In these magnetic heads, the necessary magnetic return is accomplished by the stray flux. Accordingly, the magnetic head known from these references contains substantially only a single magnet leg which faces the recording medium and which is associated with a planar writing coil winding. While a sufficiently distinct and high-frequency write signal can be generated with such a magnetic head, which is also called a single pole head, if the inductance of the coil winding is not too high, a sufficiently large read signal cannot be obtained, on the other hand, if the auxiliary pole is missing.
Due to these mentioned problems, systems with separate write and read heads are also known so that these heads can be adapted optimally to the respective function. See IEEE Trans-Magn. vol. MAG-16, no. 5, September 1980, pages 967 to 972, or vol. MAG-17, no. 6, November 1981, pages 2538 to 2540. For reading, ring heads known per se from the principle of longitudinal magnetization can be used, while recording must be carried out with the mentioned single-pole heads. These single-pole heads can have an auxiliary pole on the back side of the recording medium. Such systems for reading and recording with separate special heads adapted to the respective function, however, are relatively elaborate in their design.